Abstract
The human pathogen Campylobacter jejuni is a highly motile organism that carries a flagellum on each pole. The flagellar motility is regarded as an important trait in C. jejuni colonization of the intestinal tract, however, the knowledge of the regulation of this important colonization factor is rudimentary. We demonstrate by phosphorylation assays that the sensor FlgS and the response regulator FlgR form a two-component system that is on the top of the Campylobacter flagellum hierarchy. Phosphorylated FlgR is needed to activate RpoN-dependent genes of which the products form the hook-basal body filament complex. By real-time reverse transcriptase-PCR we identified that FlgS, FlgR, RpoN, and FliA belong to the early flagellar genes and are regulated by sigma70. FliD and the putative anti-sigma-factor FlgM are regulated by a sigma54- and sigma28-dependent promoters. Activation of the fla regulon is growth phase-dependent, a 100-fold rpoN mRNA reduction is seen in the early stationary phase compared with the early logarithmic phase. Whereas flaB transcription decreases, flaA transcription increases in early stationary phase. Our data show that the C. jejuni flagellar hierarchy largely differs from that of other bacteria. Phenotypical analysis revealed that unflagellated C. jejuni mutants grow three times faster in broth medium compared with wild-type bacteria. In vivo the C. jejuni flagella are needed to pass the gastrointestinal tract of chickens, but not to colonize the ceaca of the chicken.
Highlights
The human pathogen Campylobacter jejuni is a highly motile organism that carries a flagellum on each pole
We demonstrate by phosphorylation assays that the sensor FlgS and the response regulator FlgR form a two-component system that is on the top of the Campylobacter flagellum hierarchy
We report that FlgS and FlgR form a twocomponent signal transduction system and that this system is on the top of the Campylobacter flagellum hierarchy
Summary
The human pathogen Campylobacter jejuni is a highly motile organism that carries a flagellum on each pole. The early genes, flhC and flhD, transcribed by 70, are the regulatory proteins that control the expression of the entire fla regulon and directly activate the so-called middle genes These 70 transcribed middle genes encode structural components of the basal-body hook structure, the type III secretion system, as well as the alternative -factor FliA (28) and the anti--factor FlgM. In Helicobacter pylori, Pseudomonas aeruginosa, and Vibrio species, the fla regulon is activated by homologues of the NtrC group of response regulators (i.e. FlgR, FleQ, and FlrA, respectively) that are part of a two-component signal transduction system that works in concert with the alternative factor RpoN (54) (6 – 8). This feature enables C. jejuni to remain motile in mucus, the highly viscous environment that rapidly paralyzes other motile rod-shape bacteria [12, 13]
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